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Can Geoengineering Save the Planet?

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  • Jan 24, 2014

Two Climate Scientists Debate Pros and Cons of Climate Engineering


The concept of geoengineering, whereby humans artificially moderate the Earth’s climate, is not the sexiest sounding topic, but a small group of scientists say it might be able to prevent catastrophic global warming. In a fast-flowing and sometimes heated head-to-head climate professors David Keith and Mike Hulme set out the “for” and “against.” Keith, a geoengineering advocate, doesn’t believe that this science is a solve-all but says “it could significantly reduce climate impacts to vulnerable people and ecosystems over the next half century.” While Hulme sets out his stall in no uncertain terms: “Solar climate engineering is a flawed idea seeking an illusory solution to the wrong problem.”

Geoengineering. It’s not the sexiest sounding topic, but a small group of scientists say it just might be able to save the world.

The basic idea behind geonengineering (or climate engineering) is that humans can artificially moderate the Earth’s climate allowing us to control temperature, thereby avoiding the negative impacts of climate change. There are a number of methods suggested to achieve this scientific wizardry, including placing huge reflectors in space or using aerosols to reduce the amount of carbon in the air.

It’s a hugely controversial theory. One of the main counter-arguments is that promoting a manmade solution to climate change will lead to inertia around other efforts to reduce human impact. But the popularity of geoengineering is on the rise among some scientists and even received a nod from the IPCC in its recent climate change report.

In a fast-flowing and sometimes heated head-to-head climate professors David Keith and Mike Hulme set out the for and against. Keith, a geoengineering advocate, doesn’t believe that this science is a solve-all but says “it could significantly reduce climate impacts to vulnerable people and ecosystems over the next half century.” While Hulme sets out his stall in no uncertain terms: “Solar climate engineering is a flawed idea seeking an illusory solution to the wrong problem.”

Enjoy the debate and do add your comments at the end.

David Keith: Gordon McKay professor of applied physics (SEAS) and professor of public policy at Harvard Kennedy School

Deliberately adding one pollutant to temporarily counter another is a brutally ugly technical fix, yet that is the essence of the suggestion that sulphur be injected into the stratosphere to limit the damage caused by the carbon we’ve pumped into the air.

I take solar geoengineering seriously because evidence from atmospheric physics, climate models, and observations strongly suggest that it could significantly reduce climate impacts to vulnerable people and ecosystems over the next half century.

The strongest arguments against solar geoengineering seem to be the fear that it is a partial fix that will encourage us to slacken our efforts to cut carbon emissions. This is moral confusion. It is our responsibility to limit the impact that our cheap energy has on our grandchildren independently of the choices we make about temporary solar geoengineering.

Were we faced with a one-time choice between making a total commitment to a geoengineering program to offset all warming and abandoning geoengineering forever, I would choose abandonment. But this is not the choice we face. Our choice is between the status quo—with almost no organized research on the subject—and commitment to a serious research program that will develop the capability to geoengineer, improve understanding of the technology’s risks and benefits, and open up the research community to dilute the geo-clique. Given this choice, I choose research; and if that research supports geoengineering’s early promise, I would then choose gradual deployment.

Mike Hulme: professor of climate and culture in the School of Social Science & Public Policy at King’s College London

David, your ambition to significantly reduce future climate impacts is one of course we can share along with many others. But I am mystified by your faith that solar climate engineering is an effective way of achieving this. More direct and assured methods would be to invest in climate adaptation measures—a short-term gain—and to invest in new clean energy technologies—a long-term gain.

My main argument against solar engineering is not the moral hazard argument you refer to. It is twofold. First, all evidence to date—from computer simulations and from the analogies of explosive volcanic eruptions—is that deliberately injecting sulphur into the stratosphere will further destabilize regional climates. It may reduce globally-averaged warming, but that is not what causes climate damage. It is regional weather that does that—droughts in the USfloods in Pakistantyphoons in Philippines. Solar climate engineering in short is a zero-sum game: some will win, some will lose.

Which leads me to my second argument. The technology is ungovernable. Even the gradual deployment you propose will have repercussions for all nations, all peoples, and all species. All of these affected agents therefore need representation in any decisions made and over any regulatory bodies established. But given the lamentable state in which the conventional UN climate negotiations linger on, I find it hard to envisage any scenario in which the world’s nations will agree to a thermostat in the sky.

Solar climate engineering is a flawed idea seeking an illusory solution to the wrong problem.

DK – You are correct that climate impacts are ultimately felt at the local scale as changes in soil moisture, precipitation, or similar quantities. No one feels the global average temperature. Precisely because of this concern my group has studied regional responses to geoengineering.

In the first quantitative look at the effectiveness of solar geoengineering we found—to our surprise—that it can reduce changes in both temperature and precipitation on a region-by-region basis. This work has now been replicated by much larger study using a whole set of climate models led by Alan Robock, one of the more skeptical scientist working on the topic, and they got the same result. While there are claims in the popular press that it will “destabilize regional climates”—presumably meaning that it will increase local variability—I know of no scientific paper that backs this up.

I have no faith in geoengineering. I have some faith in empirical science and reasoned argument. It’s true that we don’t have mechanisms for legitimate governance of this technology. Indeed in the worse case this technology could lead to large-scale conflict. This exactly why I and others have started efforts to engage policy makers from around the world to begin working on the problem.

MH – David, The point here is how much faith we can place in climate models to discern these types of regional changes. As the recent report from the UN’s Intergovernmental Panel on Climate Change has shown, at sub-continental scales state-of-the-art climate models do not robustly simulate the effects of greenhouse gas accumulation on climate.

What you are claiming then is that we can rely upon these same models to be able to ascertain accurately the additional effects of sulphur loading of the stratosphere. Frankly, I would not bet a dollar on such results, let alone the fate of millions.

You may say that this is exactly why we need more research—bigger and better climate models. I’ve been around the climate research scene long enough to remember 30 years of such claims. Are we to wait another 30 years? What we can be sure about is that once additional pollutants are injected into the skies, the real climate will not behave like the model climate at scales that matter for people.

As for getting political scientists to research new governance mechanisms for the global thermostat – you again place more faith in human rationality than I. We have had more than 20 years of a real-world experiment into global climate governance: it’s called the UN Framework Convention on Climate Change. It’s hardly been a roaring success! You must be a supreme optimist to then expect a novel system of global governance can be invented and sustained over the time periods necessary for solar climate engineering to be effective.

DK: You made a very strong claim that geoengineering is zero-sum. If true, I would oppose any further work on the technology. I responded that results from all climate models strongly suggest that this is not the case. Your response was to dismiss climate models. Assume for the moment that climate models tell us nothing about regional climate response, on what then do you base your claim that solar geoengineering is zero sum – that is, that it just shuffles winners and losers?

When climate skeptics rubbish models, I defend science by agreeing if all we had was complex models I too would be a doubter; but, I then argue, that we base our conclusions on a breadth of evidence from basic physics and a vast range of observations to simple—auditable—models as well as the full-blow three dimensional climate models. Models of atmospheric circulation and aerosols developed for earth make good predictions of the climates of other planets. This is a triumph of science.

The same science that shows us that carbon dioxide will change the climate shows that scattering a bit more sunlight will reduce that climate change. How you do you accept one and reject the other?

On the other points: I am not excited by an endless round of climate model improvements nor do it think that political scientist will solve this. We need less theory and more empiricism.

MH: David, I agree that we need less theory and more empiricism. This is one of the reasons why I am skeptical that climate models are able to reveal confidently what will happen to regional climates—especially precipitation—once sulphur is pumped into the stratosphere.

I don’t dismiss climate models, but I discriminate between what they are good for and what they are less good for. Having spent nearly half of my professional life studying their ability to simulate regional and local rainfall—by comparing simulations against observations, empiricism if you will—I have little faith in their skill at the regional and local scales.

But let’s assume for a moment that climate models were reliable at these scales. Another argument against intentional solar climate engineering is that it will introduce another reason for antagonism between nations. There are those who claim that their models are good enough to precisely attribute specific local meteorological extremes—and ensuing human damages—to greenhouse gas emissions. There will be nations who will want to claim that any damaging weather extreme following sulphur injection was aerosol-caused rather than natural- or greenhouse gas-caused. The potential for liability and counter-liability claims between nations is endless.

I am against solar climate engineering not because some violation of nature’s integrity – the argument used by some. I am against it because my reading of scientific evidence and of collective human governance capabilities suggests to me that the risks of implementation greatly outweigh any benefits. There are surer ways of reducing the dangers of climate change.

This debate originally appeared on the Guardian Sustainable Business blog.

Bob Meinetz's picture
Bob Meinetz on Jan 24, 2014

David and Keith, I don’t know anyone who’s familiar with this concept and concerned about climate change who isn’t torn to some degree about the possibilities of using technology to clean up the mess we’ve made.

Like many aspects of 21st century realpolitik, the root of this temptation is an abdication of responsibility. In truth, it’s not the world we need to change, but ourselves. It’s not fossil fuels that got us in trouble but a wanton, unrelenting appetite for energy without appreciation for its consequences. Those who look to technology as a source of hope would be rewarded far more predictably by – get ready – pharmacological and genetic engineering approaches to reducing the innate anthropological need for consumption and acquisition. Addressing the problem from within is no more outlandish or far-reaching than spraying aerosols into the stratosphere, with less potential for irreversible, cataclysmic environmental effects.

But to a large extent, both are making the problem infinitely more complex than it is. If we recast the problem as one of social engineering, and can muster the necessary commitment, we have a solution within our grasp. No risky, do-or-die technological experimentation necessary.

J Elliott's picture
J Elliott on Jan 24, 2014


It’s refreshing to hear some reasonable level of debate concerning the confidence level (variability) of existing climate models and their ability to accurately predict future climate change based on the affects of the somewhat limited number of variables currently modeled.  Not to mention the enormous number of variables not understood and not currently modeled.  And, yes in theory mankind can influence the impacts of solar radiation on the planet, but what is always missing from these debates?  The enormous cost of artificially shielding the planet from the sun’s radiation.  Of course, climate researchers’ or dreamers’ are glad to accept endless government funding for geoengineering schemes that have negligible feasibility of ever being cost feasible/effective in achieving any significant climate improvements outside the normal weather/global climate variability magnitudes.   Adaptation is the only reasonable solution.  This what mankind has done since the birth of early civilizations.  It’s much more reasonable to move out of harm’s way and relocate to more sustainable environments such as small living structures outside of flood plains and well above future sea levels.


Paul O's picture
Paul O on Jan 24, 2014

I will support geo-engineering if done carefully and minimally, as we do need to prevent the climate from getting too warm. Yet we have folks who predict the most dire of consequences from global warming, and then parradoxically  oppose minimal attempts to blunt that warming.

If we could so easilly abolish Fossil Fuels, and if the abolishment of fossil fuels would or could stem GW in time before it’s too late, then great. But what are the chances of abolishing fossil fuels before it’s too late? Not very good.

It doesn’t help that some “Environmentalists” have confused the mission to stem GW with an Obsession for Wind and Solar Power exclussively, hence they oppose anything that is not wholly only WIND+SOLAR, which then parradoxically may guarrantee that GW will happen, and prevent us from molifying its worst effects.

I think the thing to do, is to forge ahead with GeoEngineering Science, while disabussing ourselves of Renewable Only mentality, and puting Global agreements in place for replacing FF sources with non-fossil sources which must include Nuclear power. Perhaps even a Global Moratorum on new coal plants.


David Lewis's picture
David Lewis on Jan 24, 2014

Paul Crutzen’s paper on geoengineering is said to have brought this entire debate out of the shadows. 

Basically, his point was that given a civilization blithely ignoring the warnings of climate scientists it was time to more openly and actively pursue options for planetary system palliative care.  He emphasized repeatedly that what is required are sufficient greenhouse gas emission reductions, however, he shared his view that such reductions appear at the moment to be “a pious wish”. 

He said that the developing world was eventually going to clean up some of what was coming out of its smokestacks, as the developed world has already done, and we’d better think about how to replace the effect of what is going to be taken out, because that smoke, i.e. aerosols, is masking the full effect of the GHG already in the atmosphere.

“Geoengineering” discussion bogs down as opponents of doing the slightest thing to so much as research techniques seem to ignore the collosal scale of what civilization ignorantly and tragically does every day. 

The proposals are simply to deal with reality as it is, and to prepare for what many fear will come next.  . 

Paul Ebert's picture
Paul Ebert on Jan 24, 2014

I am undecided about geo-engineering, but I do think there is a region of the world where Mike’s argument about it being zero-sum is invalid – the arctic.  If we were able to cool down the arctic, it could be a win for the entire planet as it might help to avoid the positive feedback mechanisms of permafrost thawing and methane hydrate release.

Robert Bernal's picture
Robert Bernal on Jan 25, 2014

I like Paul’s idea, to keep the poles cold.

Otherwise invest all efforts into developing the least expensive fossil free options. We must figure out what is intrinsically the cheapest. Machine automated solar and wind AND storage or some sort of melt down proof closed cycle nuclear. I think we all know which would be cheapest in the long run. Nevertheless we still have to machine automate batteries for electric cars, so I believe we should do ALL these options. Solar and wind should be the cheapest way up to about 20% of global energy requirements (once machine automated).

Robert Bernal's picture
Robert Bernal on Jan 25, 2014

I believe the cheapest way is “merely” extruding a few million square miles of super thin reflective film (causing A LOT a subsequent trash) to offset negative albedo. Not that it would do any good for removing the excess CO2, because the cooler temps would promote slightly less plant growth.

Robert Bernal's picture
Robert Bernal on Jan 25, 2014

Social engineering is by FAR more difficult than (most) any tech fix. Although I agree, conservation is still the cheapest (half) option. Humanity in depletion mode could be even more detrimental than excess CO2.

So, I beg to differ, it is NOT energy at fault here, just the type of energy that made us modern. This whole excess CO2 thing can be seen a test to see if we fail. If we choose limitation, we fail miserably. But if we choose to continue the path of fossil fueled depletion, the entire biosphere goes down with us. Therefore I choose nuclear energy (the only option after 20% solar and wind).

An (almost) unlimited amount of clean energy is both required for slower population growth in the developing nations AND for the power required to clean up our excess CO2 mess (via machine automation fashioned from the concept of autonomous cars???). Cruel social engineering tactics are the only other choice and I call that communism.

Paul O's picture
Paul O on Jan 25, 2014

Brilliant idea. if we could pull it off, I  don’t see a downside.

(Hmm! is there such a thing as frozen Penguins and polar Bears? It would have to be insanely cold for that to happen.)

Paul O's picture
Paul O on Jan 25, 2014

Don’t forget that we may not have enough Gallium, Neodynium, and/or other toxic rare earths,  for global sufficiency. Plus don’t forget the energy cost of the recycling effort for replacement of Billions of Solar panels and millions of Windmills that need to be decommissioned after 20-30 yrs, or the toxic juices in the Batteries for storage, which also require recycling or storage.

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